Integrated circuits (ICs) and other electronic devices often include arrangements of interconnected field effect transistors (FETs), also called metal-oxide-semiconductor field effect transistors (MOSFETs), or simply MOS transistors or devices. A typical MOS transistor includes a gate electrode as a control electrode and spaced apart source and drain electrodes. A control voltage applied to the gate electrode controls the flow of current through a controllable conductive channel between the source and drain electrodes.
Power transistor devices are designed to be tolerant of the high currents and voltages that are present in some applications. Some power transistor devices are also designed to handle radio frequency (RF) signals, such as the devices used in wireless communications and other RF power amplifier applications. One type of RF power transistor device is a laterally diffused metal-oxide-semiconductor (LDMOS) transistor. In an LDMOS device, charge carriers drift through a drift space between a channel region and the drain electrode under the electric field arising from an operating voltage applied between the source and drain electrodes.
The high operating voltages between the source and drain electrodes of an LDMOS device may give rise to the presence of high energy charge carriers in the channel region. The high operating voltages lead to high electric fields, which, in turn, increase the energy imparted to the charge carriers within the device. Device degradation typically arises from the injection of the high energy charge carriers, or hot carriers, into the gate oxide, an interlayer dielectric, or field oxide structure of the device. The resulting buildup of charge in the dielectrics from such hot carrier injection (HCI) leads to variations in operational characteristics. For example, the threshold voltage or on-state current may be modified. Performance of the device may thus be adversely affected, especially performance at high frequencies.